1. Field of the Invention
This invention relates to an electric powered vehicle or the like of the type which includes a pair of DC motors respectively coupled to independent mechanical drive systems at opposite sides of the vehicle and, more specifically, to such a vehicle which includes a means for detecting a slipping condition of one of the drive systems and a means for insuring that the other of the drive systems will propel the vehicle.
2. Description of the Prior Art
It is quite common in the operation of mines or the like to employ an AC or DC power source to generally provide power to various vehicles used in the mines. The AC power source is converted at the vehicle to DC power or the DC power is chopped at the vehicle to operate DC motors which specifically provide power to the wheels of the vehicle. Often, one DC traction motor is used to drive the wheels on one side of the vehicle and another DC traction motor is utilized to drive the wheels on the other side of the vehicle. Of course, as the vehicle goes around a corner to speed of the outside wheels and their related motor will be higher than the speed of the inside wheels and their related motor.
If one utilizes the same source of DC power for the two DC motors and they are connected in parallel, the motors would be subjected to the same voltage, but not necessarily the same current. The major advantage of such a parallel system is that full tractive effort can always be developed by either motor regardless of the speed of the other. Should the wheels on one side of the vehicle loose traction and spin out, full traction can be developed at the other side of the vehicle. On the other hand, since there is no torque sharing between the two motors, this system has inherit disadvantages. Specifically, on cornering, the inside and outside wheels attempt to turn at the same rate causing excessive currents and torques to be generated by the drive motor for the inside wheels. This can in turn cause severe loads to be produced on the drive train for the inside wheels and can cause uneven tracking of the wheels.
On the other hand, if the DC traction motors are connected in series with each other, equal torque sharing is insured since the motors are always subjected to the same current. Since the voltage across each motor can vary in a series system, this system provides a differential effect while concerning with maximized wheel tracking and optimum power efficiency. However, should the wheels on one or the other side of the vehicle loose traction and begin to spin out, very little traction could be developed by the DC motor for the wheels on the other side of the vehicle. In fact, if one set of wheels continues to slip in this manner, the vehicle might be completely demobilized.
There remains a need for providing a mine vehicle having a motor control system which employs a pair of DC motors connected in series which can utilize the inherent advantages of such a system while eliminating the disadvantages thereof. Specifically, it would be desirable to be able to detect a spin-out condition on one set of wheels and, upon such detection, to insure that the other set of wheels which are not spinning is provided with full torque to propel the vehicle.